Tridymite


Tridymite

Tridymite is a high-temperature polymorph of quartz and usually occurs as minute tabular white or colorless pseudo-hexagonal triclinic crystals, or scales, in cavities in acidic volcanic rocks. Its chemical formula is SiO2. Tridymite is stable between 870 and 1470 degrees Celsius. It has a Mohs hardness of 6.5 to 7, a specific gravity of 2.28 to 2.33 and refractive indices of nα=1.471 - 1.482 nβ=1.472 - 1.483 nγ=1.474 - 1.488. Optically, tridymite has a birefringence of < .004 and has a 2V between 40 and 90 degrees, it may have wedge, complex or polysynthetic twinning.

Tridymite was first described in 1868 and the type location is in Hidalgo, Mexico. The name is from the Greek "Tridymos" for "triplet" as tridymite commonly occurs as twinned crystal "trillings".

ee also

*cristobalite
*coesite
*stishovite

References

* [http://www.mindat.org/min-4015.html Mindat]
* [http://webmineral.com/data/Tridymite.shtml Webmineral]
* [http://mineral.galleries.com/minerals/silicate/tridymit/tridymit.htm Mineral galleries]


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Look at other dictionaries:

  • Tridymite — Catégorie IX : silicates[1] Tridymite Ochtendung, Eifel, Allemagne …   Wikipédia en Français

  • Tridymite — Trid y*mite, n. [Gr. ? threefold. So called in allusion to the supposed threefold nature of the twin crystals.] (Min.) Pure silica, like quartz, but crystallizing in hexagonal tables. It is found in trachyte and similar rocks. [1913 Webster] …   The Collaborative International Dictionary of English

  • tridymite — ● tridymite nom féminin Silice cristallisée dans le système orthorhombique, pseudohexagonale, que l on trouve dans certaines roches volcaniques …   Encyclopédie Universelle

  • tridymite — /trid euh muyt /, n. Mineral. a polymorph of quartz occurring in the form of small crystals, commonly twinned, in siliceous volcanic rocks. [1865 70; < G Tridymit, equiv. to tridym (Gk trídym(os) triple, equiv. to tri TRI + (dí)dymos DIDYMOUS) +… …   Universalium

  • tridymite — noun A rare mineral of volcanic rocks that solidified at a high temperature, with the chemical composition silicon dioxide, SiO. Tridymite is chemically identical to quartz, but has a different crystal structure. Sometimes contains sodium… …   Wiktionary

  • tridymite — tridimitas statusas T sritis chemija apibrėžtis Polimorfinė SiO₂ atmaina. atitikmenys: angl. tridymite rus. тридимит …   Chemijos terminų aiškinamasis žodynas

  • tridymite — A form of silica used in dental casting investment. [fr. G. tridymos, threefold] …   Medical dictionary

  • tridymite — [ trɪdɪmʌɪt] noun a high temperature form of quartz found as thin hexagonal crystals in some igneous rocks and stony meteorites. Origin C19: from Ger. Tridymit, from Gk tridumos threefold , because it occurs in groups of three crystals …   English new terms dictionary

  • tridymite — trid·y·mite …   English syllables

  • tridymite — n. a crystallized form of silica, occurring in cavities of volcanic rocks. Etymology: G Tridymit f. Gk tridumos threefold (as TRI , didumos twin), from its occurrence in groups of three crystals …   Useful english dictionary


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